That last bit now suggests to me we need PDL::IO::TriD::VRML, PDL::IO::TriD::OpenGL1, PDL::IO::TriD::X3D, etc: the "intermediate format" I had in mind was tuples of ("thingtype", \@needed_pdls, \%options), where "thingtype" might be "line", "triangles", etc. Now it looks like we need functions in each of those packages like line, triangles, etc, which take e.g. line($suitable_handle, \@pdls, \%options).